Research in this laboratory is presently being conducted towards the structural characterization of wellordered molecular monolayers using an integrated spectroscopic/imaging approach. We are currently using infrared spectroscopy (IR) in combination with scanning tunneling microscopy (STM) on both Langmuir-Blodgett (L-B) and self-assembled (SA) monolayer films in order to obtain compositional, conformational, and topographic information about these films. We have constructed organized lipid bilayer assemblies using a combination of SA and L-B methods which were studied using this combined IR/STM approach. Initial investigations involving phospholipid L-B monolayers on SA octadecanethiol-covered Au surfaces using the phospholipid l,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (i.e. DPPG). These studies showed acyl chain tilt angles of 5-10° within the DPPG monolayer by IR and STM. In addition, nanometer-size DPPG with hexagonal-type grain boundaries, and molecular resolution of phosphoglycerol headgroup structure within these domains, have been observed by STM. Phospholipid headgroup areas are in excellent agreement with previous X-ray diffraction studies of this system. Molecularly resolved defect structures within the headgroup framework have also been observed.
